The present invention relates to optical storage media, and in particular to an optical write once-read many (WORM) optical medium which may also be fully physically erased and re-written.
Optical media for storing data are well-known in the art. The great advantage of such optical storage media is the very high storage capacity (on the order of 1011 bits of data, or the equivalent of forty reels of magnetic tape).
These characteristics of optical media make them ideal for storing large amounts of data which must be retained for a long time, but is seldom accessed. For example, optical media are frequently used for the storage of tax records, which must be kept for several years.
Non-erasable, or write-once, optical data storage media have a plurality of bit positions, each of which can be irreversibly changed from an original state to a new state, but only one time. Thus typically the initial state of the bit position is designated as a xe2x80x9conexe2x80x9d or a xe2x80x9czeroxe2x80x9d and the xe2x80x9czeroxe2x80x9d can be overwritten with a xe2x80x9conexe2x80x9d when data is written onto the medium. Once the data has been written in a section of the medium, which may be all of the medium, that section is considered to be xe2x80x9cusedxe2x80x9d and cannot be re-used for recording new data.
This characteristic of WORM media leads to their principal disadvantage: waste. Even though the medium has very high data storage capacity, the data storage cannot be re-used.
Many attempts have been made in the art to enable the high storage capacity of WORM disk memories to be utilized efficiently in a computer system in a manner analogous to magnetic disk storage systems, wherein data in a given sector can be updated at will. All such attempts, however, have involved some xe2x80x9cmappingxe2x80x9d of either the physical addresses on the medium that are written to, or of the data already present on the medium. No known method in the art exists of transparently writing new data bits to an already-written WORM medium without mapping.
These earlier attempts have inherent problems. One key problem is how the directory or index of stored data is maintained. Without such directory information, it is impossible to selectively access and retrieve data on the disk. In one approach, when data is stored on the optical disk its location is maintained in some sort of directory or index stored on a companion magnetic floppy or hard disk. This method is obviously inefficient and susceptible to loss of the directory on the magnetic medium, making all data on the optical medium inaccessible.
Another approach has been to combine the above approach with rewriting the entire magnetic memory version of the directory onto the optical disk immediately prior to the removal of the disk or powering down of the system. The disadvantage of this approach is that it uses much disk space since the entire directory may be written onto the disk many times, and it is vulnerable to loss of the directory by power interruption before the directory has been rewritten onto the optical disk.
A third approach relies on address pointer fields associated with each data segment written onto the disk. When data is written onto a particular segment of the optical disk, the associated pointer field remains blank. When an update of the data is desired, it is written to a different segment and the physical address, i.e., the actual physical location on the disk where the updated data has been written, is written to the pointer field of the original data segment. This approach has the inherent disadvantage of long chains of pointers when data is written to the disk many times, and of wasted physical disk space caused by the pointer chains.
Another approach, exemplified by U.S. Pat. No. 4,691,299, is to xe2x80x9cmapxe2x80x9d data bits onto the physical optical disk by using a greater number of physical media bits to represent the data bits. This approach gives the appearance of being able to xe2x80x9crewritexe2x80x9d the optical disk, but in fact the actual data bits on the optical disk are not re-written. Instead, new data bits are used. Like all mapping approaches, this method has the inherent disadvantage of not fully utilizing the physical disk capacity. For example, a mapping scheme that employs four physical media data bits to write three incoming data bits can increase the apparent physical storage capacity of the optical disk by only one-third. More complex mapping schemes may result in higher disk utilization, but never 100% utilization, and at the inherent cost of processing power and delay. This method also allows the physical disk to be re-written only once.
There is thus a need for an apparatus and method for physically erasing and re-writing all physical data bits of a xe2x80x9cnon-erasablexe2x80x9d optical storage medium any number of times, without any mapping of the incoming data to existing data on the disk.
In particular, the 130 mm optical disk products available in the market fit into three categories: magneto-optic, which are writable, erasable, and re-writable; CCW WORM, which is a write-once version of magneto-optic; and ablative (or permanent) WORM, which physically alters the recording layer of the disk when writing data to the disk. These categories are further defined in International Draft Standard ISO/TEC FCD 15286:1997 (E), which specifies the following Type designations:
Type R/W: provides for data to be written, read and erased many times over the recording surface of the corresponding disk side, using the thermo-magnetic and magneto-optical effects.
Type P_ROM: provides for a part of the disk surface to be pre-recorded and reproduced by stamping or other means. This part of the disk is read without recourse to the magneto-optical effect. All parts which are not pre-recorded provide for data to meet the requirements of Type R/W.
Type O-ROM: provides for the whole of the disk surface to be pre-recorded and reproduced by stamping or other means. The corresponding disk sides are read without recourse to the magneto-optical effect.
Type DOW: provides for data to be written and read many times over the recording surface of the corresponding disk side, using the direct overwrite thermo-magnetic and magneto-optical effects requiring a single external magnetic field.
Type P-DOW: provides for a part of the disk surface to be pre-recorded and reproduced by stamping or other means. This part of the disk is read without recourse to the magneto-optical effect. All parts which are not pre-recorded provide for data to meet the requirements of Type DOW.
Type WO: provides write once, read multiple functionality using the thermomagnetic and magneto-optical effects.
Type WO_DOW: provides write once, read multiple functionality using the direct overwrite thermo-magnetic and magneto-optical effects.
The need for a new category is beginning to take shape in the marketplace: one with the technical characteristics of WORM (i.e., Types WO and WO_DOW), but with the ability to selectively delete files completely from the disk in a manner such that the data cannot later be recovered by any means. The primary application for this new product type is where data files, such as tax records, are required to be kept for a prescribed period of time, typically 7 years, but after that time period has expired it is in the best interest of the user to delete this data.
Traditional xe2x80x9cerasablexe2x80x9d optical disk products do not fully meet this need, because of the chance that data may inadvertently be over-written. Traditional WORM products do not meet this need because the data cannot physically overwritten.
The present invention satisfies this need by providing a method and apparatus such that data on an optical disk cannot be inadvertently overwritten, while at the same time providing the capability to erase completely a given data file or the entire disk surface. Additionally, new data may be written to the erased portions, taking advantage of the entire disk capacity.
A method for selectively enabling writing of data multiple times onto a write-once read-many optical disk by a host system, the disk having a disk type indicator, and each sector having a SWF field and a flag field and user data, wherein new data bits replace existing data bits in a one-for-one ratio without mapping, comprising the steps of: reading a disk type indicator; setting a firmware flag allowing writing to the disk if the disk type is erasable WORM; receiving a write command from the host system, the command specifying a sector to write to; reading the contents of the disk SWF and flag fields for the sector; overwriting all user data on the sector with all zeroes if the firmware flag is set; replacing every user data bit in the sector with a zero in a one-for-one ratio without mapping; and resetting the contents of the disk SWF and flag fields to indicate the sector is available for writing. Apparatus for selectively enabling writing of data multiple times onto a write-once read-many optical disk by a host system, the disk having a disk type indicator, and each sector having a SWF field and a flag field and user data, wherein new data bits replace existing data bits in a one-for-one ratio without mapping, comprising an optical disk drive having: a spindle motor rotating an optical disk; an optical assembly/laser generating a laser beam adapted to heat a minute region on the optical disk; a bias magnet affecting the polarity of the heated region; a write/read channel driving the optical assembly/laser and bias magnet; a write/read controller adapted to process a unique erase command and thereby controlling the optical assembly/laser and bias magnet to write every user data bit of a sector to zero in a one-for-one ratio without mapping; and a small computer system interface receiving write commands from a host system.
A principal object and advantage of the present invention is that it prevents standard disk input/output commands from overwriting data on a WORM disk, while allowing data on the WORM disk to be erased when special disk input/output commands are issued to the optical disk drive.
Another principal object and advantage of the present invention is that it completely erases data in a given sector or sector(s) on a WORM optical disk drive.
Another principal object and advantage of the present invention is that it completely erases all data in the user data area on a WORM optical disk drive.
Another principal object and advantage of the present invention is that it allows the host system to write new data to the user data area of a WORM optical disk drive with the new data bits replacing the old data bits on a one-to-one ratio with no mapping, thus using all of the available user data space on the optical disk drive.
Another object and advantage of the present invention is that it does not need chains of pointers in the user data area of the WORM drive to keep track of old data. Old data is completely replaced with new data.
Another object and advantage of the present invention is that data cannot be recovered from the WORM drive by any means once it is erased.
Another object and advantage of the present invention is that it conforms to existing international standards with only slight modifications.